WASHINGTON (AP) — Surveying a dizzying array of international crises, President Barack Obama stated the obvious: "We live in a complex world and at a challenging time."

And then suddenly, only a day later, the world had grown much more troubling, the challenges even more confounding.

The downing Thursday of a passenger plane carrying nearly 300 people spread the impact of the standoff between Ukraine and Russia far around the globe. The prospect of more Mideast casualties was assured when Israel launched a ground offensive in the Gaza Strip after efforts to arrange a cease-fire between the Israelis and Palestinians collapsed.

Yet there was a ray of hope elsewhere at week's end with the announcement that the U.S. and its negotiating partners had agreed to extend nuclear negotiations with Iran for four months rather than allowing the talks to collapse as a Sunday deadline neared.

Still, there's no guarantee of overcoming stubborn differences with Iran and reaching a final agreement. Obama also will have to find a way to stave off pressure from members of Congress, including some fellow Democrats, who see the extension as a stalling tactic by Iran and are anxious to further penalize Tehran.

"Increased economic pressure would strengthen our hand, but the administration opposes it," said Rep. Ed Royce, R-Calif., the chairman of the House Foreign Affairs Committee. "It should welcome congressional efforts to ratchet up the economic pressure on Iran."

The cascade of overseas developments comes as the American public's views about Obama's foreign policy have soured, turning what was once seen as his strength into a potential liability. For a second-term president already hamstrung on the domestic front, the world stage hardly looks like the refuge it sometimes has offered leaders in their final White House years.

Obama has said repeatedly that a world in turmoil demands American leadership, but this burst of new challenges is showing the limits of that leadership.

Investigators watch as a piece of wreckage from the Malaysia Airlines flight MH17 is transported at …

Fresh American economic sanctions on Russia couldn't stop the missile attack on the Malaysian Airlines plane, which U.S. officials believe was carried out by pro-Kremlin separatists aided by Moscow. Obama was also unable to persuade the European Union to join him in penalties aimed at Russia's most powerful economic sectors, settling instead for more tepid EU actions that strained efforts to portray a united Western front against Vladimir Putin's government.

In the Middle East, Israel began its assault in Gaza despite objections by the U.S. and the prospect of mounting civilian casualties.

The urgent international issues add to the pile of foreign policy challenges already causing headaches for the White House: Syria's persistent civil war, the rise of Sunni extremists in Iraq, China's increased aggression in territorial disputes in Asia.

The White House insists the U.S. is better off under Obama's foreign policy leadership, citing as one example his commitment to ending the wars in Iraq and Afghanistan that he inherited from President George W. Bush.

"I think that there have been a number of situations in which you've seen this administration intervene in a meaningful way that has substantially furthered American interests and substantially improved the tranquility of the global community," White House spokesman Josh Earnest said.

Obama and his advisers have tried to project a measured approach to dealing with the deepening instability. Obama stuck to plans to hold fundraisers in New York and a transportation event in Delaware on Thursday, after the plane was downed and Israel began military operations. Obama also carried on with plans to spend the weekend at Camp David, the presidential retreat in the Maryland mountains.

The strategy reflects the view of the White House that there is a danger in presidents believing they are presiding over circumstances or events that dwarf the challenges faced by their predecessors. Such thinking, Obama's aides say, can lead to overreach as presidents think that extraordinary measures are required and that their decisions can bypass the normal checks and balances.

To Obama's critics, that approach smacks of timidity and restraint that have left both foes and friends more willing to dismiss his warnings as empty threats.

For a brief moment over the past few days, it appeared the White House was on offensive, not just reacting to world events.

Obama's remarks Wednesday on the world's complexity and challenges came as he announced the most stringent American economic sanctions yet against Russia for its threatening moves in Ukraine. The package of penalties took aim at some of Russia's most powerful banks, energy entities and defense companies, and received grudging praise from Republicans.

But within 24 hours, the landscape shifted on Obama again, as reports of the downed plane surfaced.

There is some hope among Obama aides that if a Russian role in the tragedy is proved, it may push European leaders to take the tough action against Moscow they have resisted. But presidential advisers also know that the questions of additional costs and consequences will be pointed back at Obama as well.